1. Field of the Invention
The presently disclosed subject matter relates to a method for producing an L-amino acid using a microorganism, in particular, a method for producing an L-amino acid such as L-glutamic acid, L-lysine, L-threonine, L-tryptophan, or the like. These are industrially useful L-amino acids, for example, L-glutamic acid is useful as a seasoning, and L-lysine, L-threonine, and L-tryptophan are useful as animal feed additives, health food ingredients, amino acid infusions, and so forth.
2. Brief Description of the Related Art
L-Amino acids are industrially produced by fermentation using various microorganisms. For example, L-glutamic acid is produced mainly by fermentation utilizing L-glutamic acid-producing bacteria of the so-called coryneform bacteria, which belong to the genus Brevibacterium, Corynebacterium or Microbacterium, or mutant strains thereof (see, for example, Kunihiko Akashi et al., “Amino acid fermentation”, pp. 195-215, 1986, Japan Scientific Societies Press). As methods for producing L-glutamic acid by fermentation using other microorganisms, methods of using a microorganism belonging to the genus Bacillus, Streptomyces, Penicillium or the like (refer to, for example, Japanese Patent Laid-open (KOKAI) No. 5-244970), methods of using a microorganism belonging to the genus Pseudomonas, Arthrobacter, Serratia, Candida or the like (refer to, for example, U.S. Pat. No. 3,563,857), methods of using a microorganism belonging to the genus Bacillus, Pseudomonas, Serratia, Aerobacter aerogenes (currently referred to as Enterobacter aerogenes) or the like (refer to, for example, Japanese Patent Publication (KOKOKU) No. 32-9393), methods of using a mutant strain of Escherichia coli (refer to, for example, Japanese Patent Laid-open (KOKAI) No. 5-244970), and so forth are known. In addition, methods for producing L-glutamic acid using a microorganism belonging to the genus Klebsiella, Erwinia, Pantoea or Enterobacter have also been disclosed (refer to, for example, U.S. Pat. No. 3,563,857, Japanese Patent Publication No. 32-9393, Japanese Patent Laid-open No. 2000-189175).
Such methods for producing target substances such as L-amino acids by fermentation using a microorganism as described above include using a wild-type microorganism (wild-type strain), using an auxotrophic strain derived from a wild-type strain, using a metabolic regulation mutant strain derived from a wild-type strain as a strain resistant to one or more various drugs, using a strain which is both an auxotrophic strain and metabolic regulation mutant strain, and so forth.
In recent years, recombinant DNA techniques have been used in the production of target substances by fermentation. For example, L-amino acid productivity of a microorganism can be improved by enhancing expression of a gene encoding an L-amino acid biosynthetic enzyme (U.S. Pat. Nos. 5,168,056 and 5,776,736), or by enhancing the inflow of a carbon source into an L-amino acid biosynthesis system (U.S. Pat. No. 5,906,925).
An NAD(P)-dependent glucose dehydrogenase and a PQQ (pyrroloquinoline quinone)-dependent glucose dehydrogenase are both known. Furthermore, it is known that the PQQ-dependent type of glucose dehydrogenase (EC1.1.5.2) includes a soluble type and a membrane binding type, and the membrane binding type is present in the periplasmic space (space between outer membrane and inner membrane), and is widely present in enterobacteria. Hereafter, the glucose dehydrogenase present in the periplasmic space and which uses PQQ as a coenzyme is also referred to as “GCD”.
It is known that some bacteria, such as Escherichia coli, are unable to synthesize PQQ, which is a coenzyme of GCD, and therefore can express the GCD activity only when PQQ is added (FEMS Microbiol. Lett., 24, 329-333, 1984). On the other hand, such bacteria as Pantoea bacteria are able to synthesize PQQ and have a GCD holoenzyme.
As techniques concerning GCD, a method of producing cellulose from glucose by using Gluconobacter xylinus in which the gene encoding GCD is deleted (J. Biosci. Bioeng., 99(4), 415-422, 2005), and a method of producing [5S,6S]-5,6-dihydroxycyclohexa-1,3-diene-1-carboxylic acid by using an Escherichia bacterium having reduced glucose dehydrogenase activity, or an Escherichia bacterium which is inherently deficient in the glucose dehydrogenase activity (International Patent Publication WO2006/133898) are known.
However, the influence of reduction of the GCD activity of a bacterium on L-amino acid-producing ability of the bacterium has not been previously reported.